 Railroad Valley (Locke's Pond), Nevada; September 20, 1998 38° 32' 31.2" North Latitude 115° 43' 47.4" West Longitude |
 Railroad Valley (Playa), Nevada; June 14, 1998 38° 31' 46.17668" North Latitude 115° 41' 28.93099" West Longitude ± 0.116 m (4.567 in); alt 1434.849 m |
RIGHT
Left to right - Ali Abtahi, Anush Abtahi (Ali's son), Howard Tan and Tim Thompson.
The photo was taken with a digital camera (I don't know which kind) by Masao
Moriyama (aka "Masa"), a member of the Japanese ASTER science team,
on the faculty at Nagasaki University.
Ali is our instrument wizard, Howard handled the radiosondes, and I took care
of the weather station and solar radiometer (neither of which worked properly
on this trip). Anush was Ali's slave laborer. Latitude & Longitude are as
determined by
high resolution differential GPS receivers. For this trip, a whole crowd
of scientists and technicians from JPL, Japan, Canada, and the University of
Arizona were on hand. Most of us stayed in Ely. We deployed for the week, from
June 11 - 18, driving 75 miles one-way from Ely to the Valley, and back again,
every day. Another team spent the time in White River Valley, about where the
"318" symbol is located, on the map below.
These pictures were taken while I was in Railroad Valley on "validation
exercises" for the ASTER project.
Railroad Valley is in central Nevada, about 75 miles SW of
Ely, and
about 100 miles NW of
Tonopah,
just south of highway 6. If you have a good enough map of the area, it
might show Black Rock Station on highway 6, which is in Railroad Valley,
and very near Locke's Pond. Black Rock Station is a small general store
& gas station, and a favorite lunch spot whenever the ASTER gang deploys
to Railroad Valley.
The map at left shows the area west and south of Ely. Currant is where
highway 6 out of Ely comes out of the mountains and enters Railroad Valley.
The playa & Locke's Pond sites are located near the bottom of the map, about
halfway between the symbols for "6" and "318".
The ASTER Project is effort to map the earth in temperature and emissivity, from earth orbit. The instrument looks down and measures the brightness of the earth in the infrared, 5 channels in the wavelength range 8-12µ (1µ = 10-6 meters, or about 0.000039 inches). The earth's atmosphere is almost transparent at these wavelengths, but is opaque at infrared wavelengths on either side of this range. We want to see the surface through the atmosphere, so we choose this atmospheric window in wavelength to make our measurements.
Although the atmosphere is in general transparent in our window, this does not mean that the atmosphere does not affect the observations at all. Indeed, the degree of transparency varies quite a bit from place to place and time to time. The main problem is water vapor, which absorbs and scatters infrared radiation effectively. My part of the project is to work on the software that will take the atmospheric effects out of the data, and allow us to compute the infrared radiation leaving the ground, even though we can only measure what comes out of the top of the atmosphere (which for our purposes does not extend upwards beyond 100 miles, though you can actually detect the atmosphere as far away from the earth as 1000 miles). By comparing the brightness measurements in the different channels of the Reagan Solar Radiometer, we can deduce how much water and aerosol (dust or thin cloud particles) are in the atmosphere over us. We can then combine those data with other data, such as the temperature and pressure at various altitudes, to compensate the spacecraft data for the effect of the atmosphere.
These field exercises allow us to use our atmosphere compensating algorithms on images taken by satellites already in orbit, such as LANDSAT, or by special instruments, designed to simulate planned spacecraft instruments, but flown in aircraft. We know what the surface conditions were like, and if we can correctly retrieve the surface temperature and emissivity from the images, through the atmosphere we measured, then we can be confident that the software works as well on the spacecraft images that we will eventually have.
The solar radiometer in the September photo (you can click on the image for a 106 kilobyte, 300 DPI image) is designed to tell us how much water is in the atmosphere. It looks directly at the sun, and measures the difference in brightness at wavelengths where water vapor absorbs strongly, and where it does not absorb. The difference can be used to derive the total water vapor column density in the atmosphere. The radiometer is designed and built by the Atmospheric Remote Sensing Laboratory at the University of Arizona.
